This invention relates to turbine and/or compressor vanes and particularly to a mechanism by which all of the variable stator vanes in an annular row of such vanes can be locked in a desired angular orientation.
Variable stage vanes in multi-stage turbine compressors are used to address surge/stall conditions in the compressor. Typically, each vane is provided with a vane arm for rotating the vane, and the vane arms in the stage are connected to a sync or unison ring, bolted to the compressor case, that enables simultaneous rotation of all of the vanes in the stage. There are occasions, however, when testing establishes that the variable feature is not required for a particular stage of the multi-stage compressor. Converting a tested variable vane or airfoil arrangement in a selected stage to a fixed vane or airfoil arrangement in the same stage require another complete compressor test. This can be avoided, however, by locking the variable stage vanes from rotation in the respective stage, and several techniques have been utilized to effect the change from variable to fixed vanes.
For example, it has been proposed to use rigid links to lock the sync or unison ring but this approach is undesirable in that the heavy and cumbersome unison ring hardware is retained, thus also adding to the overall cost.
In order to save weight and eliminate some of the complexity of sync or unison rings, there have been attempts to eliminate the vane arm and sync or unison ring in favor of vane locks that join adjacent vanes and lock them in the selected position. See, for example U.S. Pat. No. 5,211,537. This approach is problematic in that the vanes have to be removed in order to install the vane locks, and to remove the vanes in the lower half of the turbine case, the rotor must be pulled from the case.
While there are many ways to lock a variable vane arrangement in place, there remains a need for a locking arrangement that does not alter the loaded condition of the vane during operation. In other words, the locking arrangement should load the vane in substantially the same manner as an unlocked vane during turbine operation. In addition, it would be advantageous to provide a single lock-link design for use with all vanes in the selected row of vanes.